The present invention relates to a multi-layer sliding material comprising a bearing alloy layer and a Cu-based alloy layer bonded onto the bearing alloy layer which Cu-based alloy layer acts to enhance the fatigue resistance and the wear resistance of the multi-layer sliding material.
In prior arts, a bearing used in an engine is constituted to have a back metal layer made of a steel which back metal layer has a semi-cylindrical or cylindrical shape, and a bearing alloy layer made of a Cu-based bearing alloy or an Al-based bearing alloy which bearing alloy layer is bonded onto the back metal layer. The Cu-based or Al-based bearing alloy is superior regarding the load carrying capacity, however, it is inferior regarding other characteristics required in the bearing such as anti-seizure property, embeddability, conformability and etc. To improve this problem, the conventional bearing is made to have a conforming layer provided on the bearing alloy layer so that the bearing characteristics may be improved.
Hitherto, a conforming layer provided on a Pbxe2x80x94Cu bearing alloy layer is made to contain not more than 6 mass % Cu, which is dispersed in the Pb-based matrix of the conforming layer to thereby strengthen the matrix. The advantage brought about by this Cu is disclosed in JP-A-61-266544. However, even in the case of the alloy used as the surface layer of a sliding material disclosed in this publication, the fatigue resistance and wear resistance of this alloy are insufficient when the alloy is used as the conforming layer.
The invention is achieved in taking the above-explained circumstances of the prior art into consideration, and the object of the invention is to provide a multi-layer sliding material having superior fatigue resistance and superior wear resistance.
According to the first aspect of the invention, there is provided a multi-layer sliding material, comprising a back metal layer, a bearing alloy layer bonded onto the back metal layer, and a coating layer bonded onto the bearing alloy layer, said coating layer being made of an alloy consisting of 20 to 80 mass % Pb, and the balance Cu and incidental impurities.
In the multi-layer sliding material of the invention, the hardness of the coating layer becomes high because the content of the balance Cu contained in the coating layer is in the range of 20 to 80 mass %, so that the fatigue resistance and wear resistance of the sliding material are enhanced. In a case where the content of Cu is less than 20 mass %, the hardness-raising effect of Cu becomes small with the result that the enhancement of each of the fatigue resistance and the wear resistance becomes insufficient. In another case where the content of Cu exceeds 80 mass %, the hardness of the coating layer becomes excessively high with the results that the initial conformability thereof is lowered, that the anti-seizure property thereof is also lowered, and that the fatigue resistance thereof decreases due to the decrease in the toughness of the coating layer.
Each of Pb and Cu, which are substantially evenly dispersed in the coating layer as an amorphous state prior to the use of the sliding material, comes to be precipitated as crystal grains due to heat occurring during the use thereof. Thus, the Pb crystal grains present on the surface act to enhance the anti-seizure property of the sliding material with the Cu crystal grains acting to enhance both of the wear resistance and fatigue resistance. Namely, the coating layer comes to have an enhanced fatigue resistance and an enhanced wear resistance while maintaining a good lubrication on the surface of the coating layer.
The bearing alloy layer may be made of a Cu-based alloy containing 5 to 30 mass % Pb or an Al-based alloy containing not more than 20 mass % Sn, which Cu-based alloy may further contain 2 to 15 mass % Sn and/or 0.01 mass % P and which Al-based alloy may further contain 2 to 7 mass % Si.
Sn contained in the Al-based bearing alloy layer is a soft metal similarly to Pb. It is preferred that the content of the soft metal (, that is, Pb or Sn) contained in the bearing alloy layer is less than that of the soft metal (Pb) contained in the coating layer. By selecting the contents of the soft metals in this manner, the hardness decreases in the order of the bearing alloy layer and the coating layer, so that such functions of each of them as the bearing alloy layer bears a load and as the coating layer brings about other bearing characteristics can be effectively exerted.
In the coating layer, at least one not more than 10 mass % in total selected from the group consisting of In, Sb, Sn and Ag may be added, which at least one acts to enhance the mechanical strength of the coating layer and the corrosion resistance thereof. In a case where the total amount of the at least one of the additive elements exceeds 10 mass %, the wear resistance of the coating layer is deteriorated.
Further, a conforming layer containing not less than 80 mass % Pb may be provided on the coating layer as occasion arises. Namely, since the coating layer contains a relatively much amount of Cu, the hardness thereof becomes high, so that the initial conformability thereof becomes insufficient in certain cases. In this case, by providing the soft conforming layer containing a much amount of Pb, the initial conformability of the sliding material can be improved while enhancing the anti-seizure property thereof.
Further, the conforming layer may be made of an alloy consisting of not less than 80 mass % Pb, and at least one optional element not more than 20 mass % in total selected from the group consisting of Sn and Cu.
In this case of providing the conforming layer, it is preferred that the hardness of each of the bearing alloy layer, the coating layer and the conforming layer decreases in this order. Namely, it is preferred that the Cu-based alloy and the Al-based alloy each used as the bearing alloy layer have hardness ranges of 75 to 200 Hv and 30 to 150 Hv, respectively, that the coating layer has a hardness range of 20 to 180 Hv, and that the conforming layer has a hardness range of 5 to 20 Hv. Further, it is preferred that the coating layer has a thickness of 10 to 20 xcexcm and that the conforming layer has a thickness of 2 to 10 xcexcm. In addition, a metal layer of Ni etc. may be provided, as a bonding layer, between the bearing alloy layer and the coating layer.